We propose to investigate the cellular organization of the central pattern generator for locomotion in the lamprey, a primitive vertebrate. We will employ the isolated spinal cord held under in vitro conditions. The isolated cord, when stimulated with d-glutamate, produces a pattern of stable long-lasting ventral root discharges having all the characteristics of the EMG pattern seen during intact swimming. The investigation will include a morphological and physiological analysis of the interneurons active during such episodes of so-called "fictive swimming." Conventional intracellular recording and cell marking techniques will be used. A study of the intersegmental coordination necessary for the expression of the complete pattern will include recording from and dye-injecting of phasically active intersegmental axons under conditions which distinguish ascending from descending fibers. The study will include a theoretical analysis of the cord as a system of coupled non-linear oscillators. The model that is developed will incorporate new findings as they arise. It will be tested experimentally and will be used to generate new ideas for further experimentation.